Spindle assembly air bearings

ABSTRACT

A spindle assembly includes a sleeve bearing having a number of air nozzles equi-angularly arranged about a shaft. A thrust bearing supports one end of the shaft with clearances for air support. The air nozzles generally have a frusto-conical air passage with a central bore.

United States Patent [15] 3,698,774 Saulgeot et al. 1 Oct. 17, 1972 [54] SPINDLE ASSEMBLY AIR BEARINGS [56] References Cited Inventors: Claude Anncy; Coste, Poisy, both of France Assignee: Compagnie Industrielle Des Tele 3,493,273 2/1970 Greenberg 1108/9 gmmumcanons Pans Primary Examiner-Edgar W. Geoghegan rance Assistant ExaminerF rank Susko [22] Filed: May 19, 1971 Attorney-Sughrue, Rothwell, Mion, Zinn & Macpeak [2|] Appl. N0.: 144,939 ABSTRACT [30] Foreign Application Prim"), Dam A spindle assembly includes a sleeve bearing having a I number of air nozzles equi-angularly arranged about a 7 May 20, France shaft A thrust bearing supports one end of the haft with clearances for air support. The air nozzles U-S- "Ln-308,9 generally have a frusto conical air passage a cen [5]] Int. Cl. Fl6c 19/16 tral bore" I Field of Search "308/9 9 Claims, 8 Drawing Figures nne BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention concerns a spindle assembly and more particularly, an air bearing system for the spindle assembly.

2. Description of the Prior Art In certain applications, more particularly control and machining operations requiring a high degree of precision, workpieces or the like must be mounted on spindles for rotation with a rotation precision of the order of one-tenth, or even one-hundredth, of a micron. Spindle assemblies in which conventional bearings are employed are not generally capable'of providing such precision, and this has led to the development of various bearing structures employing fluids. A fluid injected under pressure between the moving and fixed parts of such a spindle assembly should enable these portions to be maintained strictly concentric.

Devices so far proposed for carrying this out have presented a number of disadvantages. It has been observed that the arrangements for injecting the fluid under pressure can support only relatively low pressures, resulting in insufficient rigidity of the bearing arrangements produced.

Furthermore, the fluid supply nozzles must be strictly identical, which has been found particularly difficult thereby leading to pressure irregularities and faulty operation.

Also, such arrangements can generally carry only those workpieces or the like which are relatively light, so limiting their field of application.

SUMMARY OF THE INVENTION In accordance with the present invention, a spindle assembly comprises: a sleeve bearingsurrounding a shaft so as to provide a predetermined clearance between them; nozzles for supplying air under pressure to the clearance, arranged in groups in each of which the nozzles are equi-angularly spaced around the shaft axis; a thrust bearing on the shaft comprising a flange located with respective predetermined second and third clearances between a face formed on the sleeve' BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail, by way of examples only, and with reference to the accompanying diagrammatic drawings in which:

FIG. 1 is a longitudinal section through a spindle assembly; 7

FIG. 2 is a section on the line and in the direction of the arrows ll of FIG. 1;

FIG. 3 is a section on the line and in the direction indicated by the arrows llll in FIG. 1; and

FIGS. 4 through 8 show cross-sectional details of various air supply nozzles for the spindle assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, the spindle comprises a sleeve bearing 1 surrounding a shaft 3 so as to provide a predetermined clearance between them. Nozzles 2 for supplying air under pressure to this clearance are arranged in two groups, each of four nozzles equi-angularly spaced around the shaft axis. Each nozzle 2 is connected to a source of compressed air.

At one end the shaft 3 carries a flange 4 to which a workpiece or the like may be attached. A thrust bearing on the shaft comprises abearing flange 12 located with respectively predetermined second and third clearancesbetween an end face formed perpendicular to the shaft axis on the end of the sleeve bearing 1, and an abutment flange 13 attached to the sleeve bearing 1 by a circular distance piece 14 surrounding the flange. The abutment flange 13 and distance piece 14 are fastened to the sleeve bearing 1 bymeans of a set of bolts such as that shown inFIG. l.

The faces of bearing flange .12 are machined flat and perpendicular to the shaft axis, as are the opposed annular faces of the distance piece 14. The axial length of the distance piece 14 is such as to ensure the required clearances between each face of the flange l2 and either the end face of the sleeve bearing 1 or the face of abutment flange l3.

A first set of three equi-angularly spaced nozzles 16 are mounted in the sleeve bearing 1 to supply air under pressure to the second clearance, between flange l2 and the end face of sleeve bearing 1. The nozzles 16 are connected to the source of compressed air. A further set of three equi-angularly spaced nozzles 17 supply air under pressure to the third clearance, that between flange 12 and the abutment flange 13. Nozzles 17 are equally connected to a compressed air supply (not shown). v

The sleeve bearing 1 is formed with a central air release groove 6 and with similar grooves 7,8 at its opposite ends. Each of these grooves communicates with atmosphere via respective conduits 9, I0 and 11. Air is bled from the thrust bearing by grooves 18 and conduit 19.

The shaft 3 is driven by an electric motor 22 through a flexible coupling 23 linked to a journal 24 on the shaft. The flexible coupling 23 compensates for any bad alignment of the motor axis with that of the shaft 3.

The spindle assemblyis mounted on a base plate 26 through support vee 27. The motor 22 is mounted on a base 28 by rubber shock absorbers 29.

FIG. 2 shows how the nozzles 2 are equi-angularly spaced around the axis of shaft 3, being carried by the sleeve bearing 1.

FIG. 3 discloses how the nozzles 17 are equi-angularly spaced around the shaft axis.

FIG. 4 shows one of the nozzles 2. It is to be understood that the other nozzles 16 and 17 are generally similar to the nozzles 2.

The nozzle 2 comprises a generally cylindrical body 31 screw-threaded into the sleeve bearing 1, formed with an axial bore 32 the outermost end of which is connected to the compressed air source and the innermost end of which bears against an O-ring 34 and an apertured metal disc 33. The bore 32 and the aperture of disc 33 are aligned with an injection orifice 3S machined in the sleeve bearing 1.

FIG. 5 is a diametral section through the disc 33 formed with a frusto-conical aperture 36 which tapers to provide a convergent passage in the direction of fluid flow. Within the frusto-conical bore 36 is disposed a circular member 37 in the center of which, co-axially with bore 36, is formed a bore 38 of substantially constant circular cross-section, formed with a particularly regular and homogenous surface. This communicates on its upstream side with a cup 39 providing a convergent zone in the air passage. The cup 39 may be hemispherical or generally frusto-conical.

The bore 38 constitutes a thin-walled orifice in the air supply path.

FIGS. 6 to 8 show, in an enlarged scale, three forms for the aperture in disc 33. While in FIGS. 6 to 8 the apertures are formed in the disc proper, it will be appreciated that they may be formed in the same way as that shown in FIG. 5, namely with an intermediary element such as 37.

FIG. 6 shows a generally frusto-conical bore with inlet 36 and outlet 36' with, in a central region, a bore 38 of substantially constant circular cross-section. The bore 38 is formed with a particularly regular and homogenous surface. On its upstream side it communicates with a hemispherical cup 39 providing a convergent zone in the air passage.

In FIG. 7, the air passage begins with a generally frusto-conical section 36 leading to a hemispherical cup 39, a passage 38 of substantially constant circular cross-section, a further hemispherical cup 45, and ending in a generally annular zone 36'. The cup 45 forms a divergent zone in the passage, while the cup 39, as before, forms a convergent zone.

In FIG. 8 the air passage begins with a generally frusto-conical section 36, leading to a frusto-conical convergent section 46 communicating with the inlet end of a passage 38 of substantially constant circular cross-section, terminating in a divergent frusto-conical section 47. The axial length of section 47 is substantially equal to that of passage 38.

in all the forms of air passage just described, the inlets and outlets of each passage section are well rounded to avoid turbulence in the airflow.

Diametrically opposed nozzles in the sleeve bearing 1 must be rigorously identical, and all nozzles 16 must be identical, as must all nozzles 17.

The apertured disc 33, or its insert 37, are advantageously made of a dense and hard material.

The spindle assembly operates as follows:

When a load is fastened to the shaft 3, by means of flange 4, it brings about a certain eccentricity of the shaft 3 with respect to the sleeve bearing 1. A minimum clearance zone is thus formed between these two elements, bringing about a smaller gas flow and higher gas pressure than in the maximum clearance zone where flow is greater but the pressure less. The resulting lift effect tends to correct this, so as to maintain rotation with a high degree of radial precision, with regular distribution of the injected air between the shaft and its bearing structure.

The spindle assembly described above has a number of advantages.

The air supply nozzles can withstand high pressures.

. obtainable.

The spindle assembly is able tosupport heavy workpieces or the like, permitting application in a wide range of machine tools and control apparatus.

The simple structure of the spindle assembly enables the constituent components to be machined with high accuracy at a reasonable price.

What is claimed is: 1. A spindle assembly having a shaft on which workpieces are mounted comprises;

a sleeve bearing surrounding the shaft and providing a predetermined clearance between them;

first air nozzles for supplying pressurized air to the clearance are arranged equi-angularly in the sleeve bearing about the shaft;

a circular distance piece;

an abutment flange attached to the sleeve bearing by the circular distance piece; andthrust bearing means including a bearing flange, and

second and third air nozzles for supplying pressurized air to the bearing flange, the air nozzles each have a generally frusto-conical air passage with a central substantially circular cross-sectional bore communicating on its upstream side with a cup providing a convergent zone for the air supply.

2. An assembly as claimed in claim 1, in which the cup is substantially hemispherical.

3. An assembly as claimed in claim 1, in which the bore communicates on its downstream side with a further cup providing a divergent zone in the passage.

4. An assembly as claimed in claim 3, in which the further cup is substantially hemispherical. I

5. An assembly as claimed in claim 4, in which the cup has an axial length substantially equal to that of the bore.

6. An assembly as claimed in claim 5, further including a disc member, the bore of substantially circular cross-section and'the cup being formed in the disc member which is disposed within the generally frustoconical air nozzle passage.

7. An assembly as claimed in claim 6, in which the disc member is characterized by high hardness.

8. An assembly as claimed in claim 7, in which each of the air supply nozzles of the thrust bearing means is arranged to provide identical air flows.

9. An assembly as claimed in claim 8, in which the air nozzles of the sleeve bearing are arranged diametrically opposite each other and provide equal air flows. 

1. A spindle assembly having a shaft on which workpieces are mounted comprises; a sleeve bearing surrounding the shaft and providing a predetermined clearance between them; first air nozzles for supplying pressurized air to the clearance are arranged equi-angularly in the sleeve bearing about the shaft; a circular distance piece; an abutment flange attached to the sleeve bearing by the circular distance piece; and thrust bearing means including a bearing flange, and second and third air nozzles for supplying pressurized air to the bearing flange, the air nozzles each have a generally frusto-conical air passage with a central substantially circular crosssectional bore communicating on its upstream side with a cup providing a convergent zone for the air supply.
 2. An assembly as claimed in claim 1, in which the cup is substantially hemispherical.
 3. An assembly as claimed in claim 1, in which the bore communicates on its downstream side with a further cup providing a divergent zone in the passage.
 4. An assembly as claimed in clAim 3, in which the further cup is substantially hemispherical.
 5. An assembly as claimed in claim 4, in which the cup has an axial length substantially equal to that of the bore.
 6. An assembly as claimed in claim 5, further including a disc member, the bore of substantially circular cross-section and the cup being formed in the disc member which is disposed within the generally frusto-conical air nozzle passage.
 7. An assembly as claimed in claim 6, in which the disc member is characterized by high hardness.
 8. An assembly as claimed in claim 7, in which each of the air supply nozzles of the thrust bearing means is arranged to provide identical air flows.
 9. An assembly as claimed in claim 8, in which the air nozzles of the sleeve bearing are arranged diametrically opposite each other and provide equal air flows. 